Most motor vehicles have in recent years been equipped with on-board computers connected to sensors located in various systems in the motor vehicle, for example the engine, the exhaust system, and the like.
The Society of Automotive Engineers (SAE) has set standards which include a standard connector plug and a set of diagnostic test signals that technicians use when adjusting or repairing the motor vehicle. The standard connector plug and set of test signals, today, is known collectively as OBD-II (On-Board-Diagnostic, version 2) which applies to all cars and light trucks built after Jan. 1, 1996.
The on-board computers may also be coupled through the OBD-II interface to an on-board equipment containing a wireless modem, and thence to a wireless communications network to enable interested parties to remotely obtain diagnostic and other information from the motor vehicle. The applications for accessing the vehicle on-board computers remotely include highway monitoring of emission levels, and surveillance of fleet vehicles from a central location for purposes of performance tracking and maintenance scheduling.
Depending on the application, various ways are possible in which the wireless connectivity between the vehicle and a computer host at a monitoring location (to be referred to as the central host) can be achieved. For example the wireless modem may be configured to operate in the manner of a cellular telephone, and use the cellular telephone network to connect to any central host equipped with access to the telephone network. Similarly, the wireless modem may be configured to access the central host over a Wide Area Network (WAN), for example the internet. A system for transmitting, collecting and displaying diagnostic and operational information from one or more motor vehicles to a central server connected to a wide area network, is described in U.S. Pat. No. 6,295,492, issued to Lang, et al.
A problem of access may arise, due to the reliance on a single wireless network between the vehicle and the central host. As a practical matter, and due to the nature of being a vehicle, the vehicle may travel between many locations. The use of a single, virtually ubiquitous, wireless network is possible in principle (viz. the cellular telephone network, or a satellite based network), but the use of such a network for frequent and regular access to a potentially very large number of vehicles is both expensive and wasteful of resources.
This problem may be circumvented by deploying a number of remote computers (such as reference 27 in FIG. 1 of the U.S. Pat. No. 6,295,492 cited above), connected to the central host by conventional means, e.g. the land-line based internet. Each remote computer serves as a wireless gateway (WAP or wireless access point) to a localized wireless network. The Institute of Electrical and Electronic Engineers (IEEE) Standard 802.11b describes protocol for use in a Wireless Local Area Network (WLAN). If the system is based on the IEEE 802.11b Standard, the on-board modem accesses the nearest compatible remote computer and through it achieves data communication with the central host.
Other patents describing similar remote vehicle diagnostic systems, or aspects of such systems, include; U.S. Pat. No. 6,604,033, issued to Banet, et al.; U.S. Pat. No. 6,611,740, issued to Lowrey, et al.; and U.S. Pat. No. 6,636,790, issued to Lightner, et al.
It is generally understood that WLANs of the kind described above have a very limited geographic reach, on the order of a few 100 meters at most. There is not a continuous geographic coverage of WLANs, and a vehicle may frequently be outside the reach of any WAP. Nevertheless, WLANs for the purpose of providing wireless access for vehicles for remote performance monitoring, diagnostics, or exhaust emissions performance checks, may be established at vehicle repair facilities, in parking lots, at high way toll plazas, etc. Furthermore, not every WLAN is designed or intended to operate with all vehicles. In general, WLAN devices (i.e. the vehicle's on-board computer) must be authorized and be registered by the WLAN master (also referred to as WLAN gateway) before communication is possible.
The vehicle's on-board computer may store vehicle data in its memory during periods when the vehicle is not within reach of a designated WLAN. In a conventional application, for example when the vehicle is in a repair shop being serviced, there is no problem collecting all data. However in a general surveillance or remote monitoring application, where the vehicle is free to roam, the driver may not even be aware of the data collection taking place, or of the boundaries of a WLAN the modem in the vehicle is currently accessing. In this case, the time for wireless accessibility may be short, frequently interrupted, and occur at a number of different WAPs successively.
A method, directly applicable to vehicle telemetry is disclosed in Canadian Patent 2,414,126, issued to Nader, et al. In this system a specific protocol (Internet Protocol IP version 6) is used which can provide a virtual continuous data path (connection) between the vehicle and the central host regardless of which WLAN the vehicle is currently accessing. While providing an elegant way of “hiding” the problem, thus possibly simplifying software design at the host, this solution does not address the practical aspects of providing continuity of information using a generally available protocol (IP version 4) nor does it take into account the uncertain, often intermittent, presence of vehicles within reach of a WLAN.
There exists thus a problem to ensure continuity of the effective data communication between the vehicle and the central host.
This problem is partially solved, in a different context (hand-held personal computing devices, rather than vehicles) in a system described in U.S. Pat. No. 5,564,070, issued to Want, et al. In this system, the main flow of information is from the central host to the mobile device. Stationary computers, attached to a WLAN gateway, are used to temporarily hold or buffer data from the central host and destined for the mobile device, while the mobile device is out of reach for brief periods of time.
In the case of the motor vehicle telemetric system however, the main flow of information is the reverse, from the vehicle to the central host. The method described in the above cited U.S. Pat. No. 5,564,070 for providing continuity of communication is thus not directly applicable to the problem of providing continuity of information in a motor vehicle telemetric system.
What needs to be developed is a method for providing continuity of information in a vehicle telemetric system over localized wireless networks (WLANs), to permit a central host to collect diagnostic and other data from a vehicle, even when wireless access is intermittent.